"device" : "0-1" specifies, that this one is the setting for Card 0 and 1 aka both R9 280X
Well I just learned something new today thanks
Those need the same settings, it does not change the output whether i run one or two cards with this setting. The 290 only needs one gputhreat so it is on another cgminer instanz.
However this is not entirely true: they may both be R9 280X, but being from different brands they need different settings.
Just as a personnal example:
I use 1080Mhz core and 1500 mhz Mem on my Asus R9 280X for 750Khs, but if I use the same settings on my MSI R9 280X, the hashrate is nowhere near 700Khs, it only hashed well at 1030Mhz core.
I don't know what are the fine tuning for Powercolor and Sapphire